Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and a transfer voltage control program.
Description of the Related Art
In electrophotographic type image forming apparatuses, a technique of providing a cleaning apparatus on a latent image bearing body or an intermediate transfer body is known. This technique is provided for the purpose of removing residual toner such as untransferred toner and transfer residual toner on the latent image bearing body or the intermediate transfer body. As an exemplary cleaning apparatus, a blade cleaning system is known. The blade cleaning system uses a flat plate-shaped cleaning blade formed of an elastic body. The cleaning blade is abutted against a surface of the latent image bearing body and of the intermediate transfer body, thereby removing residual toner on the latent image bearing body and on the intermediate transfer body.
In recent years, in the electrophotographic type image forming apparatuses, there have been demands for micronization of toner particles in view of achieving higher image quality. As methods for creating micronized toner particles, for example, polymerization methods including emulsion polymerization and suspension polymerization are known. However, the smaller the toner particles become, the greater adhesion occurs between the toner particles and the latent image bearing body, causing difficulty in removing residual toner on the latent image bearing body. In particular, in a case where toner is generated by using polymerized toner produced by polymerization, the shape of the toner particle is substantially spherical. In this case, the toner particle tends to roll on the latent image bearing body and pass through the cleaning blade. Due to this tendency, a cleaning failure is likely to occur, leading to increased difficulty in removing residual toner on the latent image bearing body.
Generation of the toner passing through the blade would cause a toner aggregate to be formed around initial toner as a core on the latent image bearing body. This would cause a white spot (granular noise) to be formed at a portion where a solid image is printed.
In order to cope with a quality issue of “granular noise”, cleaning is currently performed in a state where lubricant is supplied on the latent image bearing body so as to form a lubricant coating to decrease adhesion between the toner particles and the latent image bearing body. As a method of supplying lubricant on the latent image bearing body, a lubricant application method is known. The lubricant application method allows a brush to be abutted against a stick-shaped lubricant so as to scratch a portion of the lubricant and then supply the portion of the lubricant to a surface of the latent image bearing body.
According to the lubricant application method, the portion of lubricant supplied onto the surface of the latent image bearing body by the brush comes in contact with a developing sleeve of a developer container, or the like. By this contact, the portion of lubricant is scratched from the surface of the latent image bearing body and taken into the developer container. The lubricant taken in is mixed with the toner while being conveyed inside the developer container and re-supplied to the latent image bearing body together with the toner supplied at the developing unit. In printing a low area ratio (printing ratio) image for which a toner consumption amount is small, the amount of toner used for developing would be reduced. Accordingly, the amount of lubricant re-supplied with the toner would be reduced. Meanwhile, supply of lubricant onto the surface of the latent image bearing body from the brush and scratching of lubricant from the surface of the latent image bearing body occurring at the developing unit are not very much influenced by the toner consumption amount or the area ratio. Accordingly, continuing printing of low area ratio images would increase the amount of lubricant inside the developer container. Conversely, continuing printing high area ratio images would decrease the amount of lubricant inside the developer container. In short, in the lubricant application method, the amount of lubricant in the developer container varies depending on the toner consumption amount.
For example, when the amount of lubricant inside the developer container after a low area ratio image has been printed, the ratio of the lubricant to the toner inside the developer container increases. In this case, the amount of lubricant that moves onto the latent image bearing body together with the toner increases at an image portion (portion to which toner is attached due to a potential difference at the developing unit and developed). The toner on the image portion including a large amount of lubricant is transferred at the transfer unit to the intermediate transfer body. As a result, a portion with a large amount of lubricant is generated also on the intermediate transfer body.
When such a portion with a large amount of lubricant is generated on the intermediate transfer body, the large amount of lubricant on the portion would be aggregated by incorporating foreign objects such as paper dust, so as to form an aggregate. The aggregate is conveyed on the intermediate transfer body and caught at a portion between the intermediate transfer body and the cleaning blade provided on the intermediate transfer body. When the aggregate is caught, an edge of the cleaning blade is pushed up, causing a failure in retaining an abutted state between the cleaning blade and the intermediate transfer body. This causes toner particles to pass through the cleaning blade in the vicinity of the portion where the aggregate is caught, leading to occurrence of a cleaning failure. Regarding this issue, there is a known technique (refer to JP 2010-256629 A). According to JP 2010-256629 A, lubricant is applied to the latent image bearing body, and then, according to a result of detection of a friction coefficient of the intermediate transfer body, the toner input amount to the intermediate transfer body is controlled, thereby controlling the amount of lubricant on the intermediate transfer body.
Unfortunately, however, the technique described in JP 2010-256629 A controls the toner input amount to the intermediate transfer body. Therefore, the technique described in JP 2010-256629 A is not executable in an image region where a usual image corresponding to a document image is formed, but only executable suitably in a non-image region other than the image region. For example, execution of the method described in JP 2010-256629 A at a time of transfer of an image in the image region might influence the quality of the image to be formed due to a change in the toner input amount.